Contact finger with grooves

ABSTRACT

A contact finger ( 4 ) includes a connection member ( 5 ) and a contact member ( 6 ). The connection member is connected to one end of a cable, while the contact member ( 6 ) is intended for contact with a corresponding contact member ( 6 ) on a second contact finger ( 4 ). A transverse, ridge-shaped portion is provided at the front end portion of the contact member ( 6 ). The contact member ( 6 ) is moreover provided with a series of grooves ( 10 ) for improved contact efficiency. A contact device according to the present invention includes a contact finger in accordance with the above.

TECHNICAL FIELD

The present invention relates to a contact finger comprising aconnection member for connection to one end of a cable and a contactmember for contact with a corresponding contact member on a secondcontact finger, a transverse, ridge-shaped portion being provided at thefront end of the contact member. The present invention also relates to acontact device.

BACKGROUND ART

Contact fingers and contact devices in accordance with above arepreviously known in the art. More precisely, contact devices arepreviously known in the art in particular for high current strengths,where the contact devices are intended to be connected to the end of acable for interconnection of one or more cables to one another. Thecontact devices comprise an outer housing, typically manufactured fromplastic, contact fingers for the actual electrical connection, and ametal spring associated with each contact finger in order to generatesuch a force on each respective contact finger that they, in theconnected state, are biased towards one another for maintaining goodcontact, whereby sparking or undesirable overheating because of adefective contact between the contact fingers is intended to be avoided.

Those parts that are intended to be in direct physical contact with oneanother moreover display a standardised design so that contact devicesfrom different manufacturers may marry together with one another.

The springing which was mentioned above has thus hitherto been used torealise a good contact between the contact fingers. Certainly, thisfunctions satisfactorily, but at high current strengths it has provedthat the springing is not always sufficient to entirely prevent sparkingor undesirable overheating. The term “higher current strengths” is takenin this context to signify current strengths that are higher than thosefor which the contact device in question is classified. At the sametime, the stiffness of the metal spring cannot be further increased fora classification for increased current strength while retaining the samephysical dimensions, since interconnection and disconnection of thecontact devices which, to some degree, take place against the action ofthe spring, must still be possible. The reason for the defective contactat higher current strengths is thus assumed principally to beinsufficient contact pressure or otherwise a far too limited contactsurface area.

A further problem is that the contact fingers, when they are connectedeach to a cable end, can be affected thereby when the contact devicesare moved, in particular if the cables are heavy and stiff. In suchinstance, the contact fingers may slip in relation to one another and inthe even of unevenness, play may readily occur between them. Nor is theposition of the contact fingers in relation to one another or to thecontact housing a matter of absolute certainty.

Another problem may be random and unpredictable unevenness in thematerial, which may possibly have occurred during manufacture. It may bethe contact fingers themselves that are uneven, so that contact onlytakes place at some individual point instead of along a line, which isintended. Possibly, the contact fingers may flip around such a contactpoint, at least in the even of insufficient contact pressure, which willgive rise to problems involving sparking and undesirable overheating asdescribed above.

The contact springs may also partly contribute to these undesirableproperties, in that they do not exactly correspond to the establishednorms and requirement specifications and, as a result, deliver a springforce which is not uniform throughout the entire width of the contactfinger.

While these problems may in principle be circumvented by replacing anexisting contact device with a higher classification as regards currentstrength, this is not often desirable, on the one hand for reasons ofspace and on the other hand for reasons of cost.

Problem Structure

There is thus one object of the present invention to realise a contactfinger and contact device, respectively, where sufficiently good contactis obtained in order to make for use at higher current strengths thanhas hitherto been possible, at the same time as the outer dimensions ofthe contact device are maintained unchanged.

Solution

The object forming the basis of the present invention will be attainedconcerning the contact finger if this is characterised in that thecontact member is provided with a series of grooves for improved contactefficiency.

Further advantages will be attained if the contact finger is moreovergiven one or more of the characterising features as set forth inappended subclaims 2 to 8.

Concerning the contact device, the object of the present invention willbe attained if this includes a contact finger in accordance with theforegoing.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detailhereinbelow, with reference to the accompanying Drawings. In theaccompanying Drawings:

FIG. 1 is a perspective view of a contact housing in which at least onecontact finger according to the present invention may be disposed;

FIG. 2 is a perspective view of one preferred embodiment of the contactfinger according to the present invention;

FIG. 3 is a straight side elevation of the contact finger according toFIG. 2; and

FIG. 4 is a perspective view of the contact finger according to FIGS. 2and 3 from another angle.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows the housing 1 for a contact device which includes a contactfinger 4 according to the present invention. The housing 1 which isshown in the Figure may include two contact fingers 4 according to thepresent invention, and these are accessible through the openings 2 inthe end of the housing 1 facing towards the observer of the Figure. Thehousing 1 which is shown in the Figure is to be considered exclusivelyas an example and the present invention also encompasses contact deviceswith both a single contact finger and with three or more.

Two identical houses 1 marry together to one another so that the contactfingers 4 in each respective contact device can come into contact withone another. In order for this to be possible, two contact devices mustbe turned to face towards one another so that the ridges 3 on the onehousing 1 fit in the openings 2 on the other, corresponding contactdevice. The contact devices are identical and must be turned so as to beconnected together and it is not physically possible to connect themtogether incorrectly.

Contact devices of the type illustrated in FIG. 1 have different fieldsof practical application depending on the current strength for whichthey are intended, but are often used in applications with relativelyhigh current strengths, typically of the order of between 50 and 600 Adepending on size, with voltages of up to 600 V. One example of such apractical field of application is the charging of battery poweredelectric trucks for indoor use.

FIG. 2 shows a contact finger 4 according to the present invention. Themain parts of the contact finger 4 are a connection member 5 and acontact member 6. The connection member 5 functions for connection tothe end of a cable, while the contact member 6 is intended to be incontact with the contact member 6 on a contact finger in that contactdevice together with which the first contact device is interconnected.The material in the contact finger 4 is preferably a material possessingextremely good conductivity, for example pure copper, pure silver orsilver-plated copper. Both of the materials are advantageouslysurface-treated so as to prevent scratches and oxidation in the surfacelayer which cold possibly lead to deterioration in contact.

The connection member 5 is, in the preferred embodiment, in the form ofa tube which is closed at its inner end, i.e. that end which connects tothe contact member 6. On connection of the connection member 5 to acable, one end, where the insulation has been stripped off a distanceslightly less than the length of the connection member 5 is passed intothe connection member 5. Thereafter, the connection member 5 is deformedor crimped so that it is fixed and remains in position on the cable.

The contact member 6 includes, as is also visible in FIG. 3, aridge-shaped portion 7 at its outer, front end. The ridge-shaped portion7 is transverse in relation to the longitudinal direction of the contactfinger 4. The ridge-shaped portion 7 on each respective contact finger 4is to be “passed” by the contact finger 4 in the opposing contact devicein order to reach an interconnected position with good contact betweenthe contact fingers 4. In such instance, the two contact fingers 4 areintended to spring away a distance transversely of the direction ofmovement on the interconnection, from their final interconnectedposition before this latter may be assumed.

The planar portion 8 is the inner portion of the contact member 6. It isunlikely that this area will be used for direct contact with anothercontact finger 4 on the interconnection of two contact members, but thisportion is also manufactured of the same material and with the samesurface treatment as the remainder of the contact finger 4. Between theplanar portion 8 and the ridge-shaped portion 7, there is a transversedepression 9 which is not to be found on prior art contact fingers 4.The configuration of the depression 9 is complementary to that of theridge-shaped portion 7, so that a larger abutment area andconfigurational engagement will be obtained on the front portion of thecontact finger 4.

The front portion of the contact member 6 is grooved with a number ofgrooves 10. The width of the grooves 10 is equal to or greater than thedepth of the grooves 10 in the preferred embodiment. The width of thegrooves 10 is substantially of the same order of magnitude as the space11 between them. The grooves are disposed at an angle to thelongitudinal axis of the contact finger. The obliquely inclined grooves10 will, on an interconnection with a similar contact finger 4, entailthat contact between the two contact fingers 4 takes place in a networkof contact points, i.e. in those regions where the spaces 11 intersectone another. Even if contact does not take place in the grooves 11,their presence will nevertheless lead to an improved contact and therebyless heat generation. Probably, this is because the pressure in thecontact areas has increased, since the total contact area is reducedwhile the force delivered by the spring means on the contact fingers 4is substantially constant. The contact between the two contact fingers 4will thereby be more reliable and the risk of play and sparking isreduced. It is hereby possible to increase the current strength withoutany simultaneous increase in the generation of heat.

The appearance of the depression 9 is particularly well apparent fromFIG. 3. Its profile largely corresponds to the profile of theridge-shaped portion 7 which is reminiscent of a length of a sinuscurve. The profile of the ridge-shaped portion 7 and the profile of thedepression 9 are largely complementary to one another, which impliesthat a contact between them also takes place along the flank 12 in thetransition between the ridge-shaped portion 7 and the depression 9.Moreover, abutment takes place not only along a line at the highestpoint of the ridge-shaped portion 7, but over a larger zone along thebottom and defining surfaces of the depression 9. Contact may possiblynot take place over a completely unbroken surface if the grooves 10 aredisposed on the contact finger 4, but in such an event the abutmentgives an increase of the number of contact points in the network whichis formed between the slanting grooves. The flank 12 is, like theridge-shaped portion 7 and the depression 9, provided with grooves 10 inthe preferred embodiment.

The match between the profile of the ridge-shaped portion 7 and theprofile of the depression 9 also gives a configurational interlock whichis considerably more reliable than has hitherto been possible, andreduces the risk of movement between the two contact fingers 4 andthereby of play or clearance between them, or of unintentionaldisconnection.

A further distinguishing feature in the contact finger 4 according tothe invention is the presence of a longitudinal slot 13 through thecontact member 6. This slot 13 provides in itself an effect on thecontact efficiency, regardless of whether the contact finger 4 isprovided with grooves or not. The reason for this is probably that amaterial unevenness at a point on one side of the slot 13 need notnecessarily entail that play between the contact fingers 4 occursthroughout the entire contact member 6.

In the preferred embodiment, a contact finger 4 is shown with a singleslot 13, but variations on this theme are conceivable, such as a contactfinger 4 completely without a slot 13, but also with two or even moreslots 13.

On that side of the contact member 6 which is turned to face away fromthe corresponding contact finger 4 and, thus, is not to be in contactwith another contact finger 4, there is disposed a heel 14 along theentire width of the contact finger 4. The heel 14 is intended forengagement with the previously mentioned contact spring which entailsthat the contact fingers 4 are resiliently disposed in the housing 1.Corresponding heels 14 are also disposed on contact fingers of prior arttype. In connection with the heel 14, there is, however, a depression orrecess 15. The material which has been omitted on the making of therecess 15 is preferably used to widen the contact finger 4 and therebyprovide room for a further additional few contact points withsubstantially the same total quantity of material included.

The depression or recess 15 may also be utilised for a material savingin relation to the prior art contact fingers without any appreciablereduction taking place of the stability of the contact finger 4.

In practical trials with one type of contact device, it has proved thatcontact fingers according to the present invention have such a low heatgeneration while in operation that contact devices with such contactfingers have been able to be classified for use in current strengths ofup to 225 A, compared with 175 A for a corresponding prior art contactdevice.

The above-described advantages and the good contact between two contactfingers 4 according to the present invention are attained in idealconditions, i.e. when two identical contact fingers 4 according to theinvention are in contact with one another. However, a satisfactoryresult will also be attained as regards contact efficiency also when onecontact finger 4 according to the present invention is interconnectedwith a prior art contact finger. Probably, performance would liesomewhere between the performance for two prior art contact fingers andtwo contact fingers 4 according to the present invention. However, careshould be taken to ensure that the contact efficiency is notoverestimated, but the point of departure should be that the highestpermitted current strength is the lowest of those disclosed for contactdevices according to the new and prior art technologies, respectively.Interconnection of contact devices of different classifications is ingeneral not permitted for reasons of safety and, as a result, it ispossible to provide contact devices with different mechanical obstaclesagainst interconnection, such as locking devices which only permit theinterconnection between identical contact devices.

Description of Alternative Embodiments

The present invention may be varied in a number of different respectswithout to that end deviating from the inventive concept as hereindisclosed. For example, the width, depth, density and cross sectionalprofile of the grooves may be different from those shown on the Drawingsand described above.

In the preferred embodiment, the contact fingers have been described ashaving both grooves 10 and a cross-sectional profile which consists of aridge 7 and a depression 9. It is fully possible to provide a contactfinger with only two of these characterising features, i.e. to provide acontact finger of conventional cross-sectional profile with grooves, oralternatively to provide a smooth contact finger with thecross-sectional profile according to the present invention.

Another method of varying the invention is to cause the ridge-shapedportion 7 and the depression 9 to change places, i.e. to position thedepression 9 outermost on the front portion of the contact finger 4 andthe ridge-shaped portion 7 inside it. By such means, there will berealised a substantially equally large contact area as in the preferredembodiment. Possibly, protection against unintentional disconnection maybe slightly poorer, since the ridge-shaped portions 7 do not pass eachother on interconnection.

Yet another method of varying the present invention is to cause thegrooves to intersect one another on one and the same contact finger 4 sothat a diamond pattern is formed throughout the entire or parts of thegrooved area. When two such contact fingers are interconnected, the twodiamond networks will together form yet a further diamond network which,in most cases, is “denser” than each one of the diamond networksindividually, with a large number of contact points.

As was mentioned above, it is also possible to vary the number of slotsor incisions 13 in the contact member 6 and also their length.

The present invention may be varied further without departing from thescope of the appended Claims.

1. A contact finger comprising a connection member (5) for connection toone end of a cable and a contact member (6) for contact with acorresponding contact member (6) on a second contact finger (4), atransverse, ridge-shaped portion (7) being provided at the front endportion of the contact member (6), characterised in that the contactmember (6) is provided with a series of grooves (10) for improvedcontact efficiency.
 2. The contact finger as claimed in claim 1,characterised in that the grooves (10) are disposed on and inassociation with the ridge-shaped portion (7).
 3. The contact finger asclaimed in claim 1, characterised in that the grooves (10) are disposedin two or more series of mutually aligned grooves (10), the series atleast partly overlapping one another so that a diamond pattern isformed.
 4. The contact finger as claimed in claim 1, characterised inthat the grooves (10) are slanted so that they are angled in relation tothe longitudinal axis of the contact finger (4).
 5. The contact fingeras claimed in claim 1, characterised in that a transverse depression (9)whose configuration is complementary to the ridge-shaped portion (7) isdisposed in association with the ridge-shaped portion (7), theridge-shaped portion (7) on one contact finger (4) being insertable inthe depression (9) on a corresponding contact finger (4) and vice versa.6. The contact finger as claimed in claim 1, characterised in that arecess (15) is provided on that side of the contact member (6) which isopposed to the ridge-shaped portion (7).
 7. The contact finger asclaimed in claim 1, characterised in that at least one longitudinal slot(13) divides the contact member (6) in its longitudinal direction. 8.The contact finger as claimed in claim 1, characterised in that theconnection member (5) is tubular.
 9. A contact device comprising atleast one contact finger (4) as claimed in claim 1.